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Old 07-14-2021, 07:54 PM
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Question Who drives a 455 withFlattops and Iron Ram Air Heads?

Working my Spare 455 +030, and have flattops and "48s".
BOP 1-piece Rear Seal in, Forger 4.21" Stroke, 3.25" Mains TQ'd with Factory Bolts. 1973 2-Bolt Block.

Wondering what Octane is needed to drive on the Street THESE DAYS.
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12.24/111.6MPH/1.76 60'/28"/3.54:1/SP-TH400/469 R96A/236-244-112LC/1050&TorkerI//3850Lbs//15MPG/89oct

Sold 2003: 12.00/112MPH/1.61 60'/26"x3.31:1/10"/469 #48/245-255-110LSA/Q-Jet-Torker/3650Lbs//18MPG 94oct
Sold 1994: 11.00/123MPH/1.50 60'/29.5"x4.10:1/10"/469 #48/245-255-110LSA/Dual600s-Wenzler/3250Lbs//94oct
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Old 07-14-2021, 08:29 PM
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You can't run flat tops, 4.21 stroke with 48s on pump gas. Never going to work.
I would not push it past 9.5-1 static on 91 octane.
Even back in 1970 with PMD 455s with 64 heads, 10-1 CR the dealerships were getting come backs from customers breaking pistons not running premium fuel. Not sure what the octane rating on premium was back in 1970 but I bet it was higher than 91-93.
Whatever you do, get a custom pump gas cam to give your engine a chance of living.

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Old 07-14-2021, 11:21 PM
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Do you have a local source for E85 might be a way to go in a more economical fashion

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Old 07-16-2021, 10:04 AM
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Seems like there are certain quench ranges that cause issues too. For some reason quench from .070” to .09” range is worse than .09 to .14”. Then after sometime after .14” issues start to show up again. See that on open chamber stuff to where we milled the heads and quench end up in that .070” -.090” range, has some extra issues, each engine acts different though. Not sure the RA heads will be much different, my guess is they are going to respond similarly, I would keep out of that .07-.090 quench range.


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Old 07-15-2021, 12:37 AM
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Not the exact same setup, but I had a .060 over 455 with 62 heads and flat tops. Ran on 93, but was right at the edge of not being happy.

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Old 07-15-2021, 03:20 AM
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I've run as much as 10.1:1 with a 4.25" crank and 4.181" bore using 6X heads but you gotta' stay on top of the tune to run 92 octane with it. There's no setting the timing and adjusting the carb and then forgetting about it for a couple of months.

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Old 07-15-2021, 05:19 AM
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Back in the day, I ran a 455 with 62 heads. 230 cam. 225 cyl press. That thing was not happy at all unless you ran race gas or 100LL that I got from the airport.

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Old 07-15-2021, 05:32 AM
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Find some 96s and let it be happy.
Looks like a few guys ran 62s and had issues. They are about 5cc larger than 48s. 48s, zero chance.
Thing is, if you push it all that has to happen is a bad load of gas or a real hot day and you have a blown head gasket or worse.

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Old 07-15-2021, 07:18 AM
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All of the above make sense, and the most relevant tells me it is harderin 2021 to ride the combo ping-free bubble than it was in the early 90s.

See here's the thing; sold my 5Cs to a fella (oh he's happy), and only have the 48s andflattops. Flattops are part of a Crank balance.

So, i need 7M5, 4x, 5C, 6X or E or KRE, or Speedmaster to make a "Combo". Well, i hate to bare the 48s to dress up the low compression iron. Speedmaster?...! roundports?

Thinking to build the high-compression deal, break-in cam and rings, then remove the Top-end 48s For Sale as ported and fresh running set of heads, to recoup the low compression set.


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Old 07-15-2021, 10:23 AM
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Just my opinion. But if I have a set of high compression heads and spent a bunch of time and money on with port work, valves, guides , ect….I would take a hard look at cutting a symmetrical dish in the flat tops to drop the compression some and run the 48s over starting over again on some lower compression heads. If it is a balanced rotating assembly I would figure the mass loss from the dish and figure the effects on balancing, might be ok yet. That or buy appropriate pistons and maybe sell those pistons and get some pistons that will put the compression in a range that works better. I don’t like doing things twice but I would rather do that than start on another set of heads. Here it is $170 to rebalance, that won’t go very far rebuilding heads, let alone port work, even if it is a DIY scenario. Our best pump gas results (so far) have been with symmetrical dished pistons over flat tops, D shape, or domes. Maybe more factors at play there though. FWIW

I mostly shoot for between 10 to 11 compression on my cast iron heads with a lot of port work in Pontiacs 450 + cid for 87 to 91 octane. FWIWz…I don’t think I am quite to the point I am at 11:1 for 87. I was looking at the new Progression Ignition distributer that you can modified the timing curve and it connects via blue tooth with a smart phone. I think that is my next step to get to 87 on the 11:1 street engines. But I think I will carry the oem HEI in the trunk, just in case…Lol.

Totally stock d port 455 on 91 octane we have been a 10.4 SCR. Might have ran on 87, never tried it. Cam was big for the head flow, it didn’t run great. It dropped the DCR to low for the RPMs the cam wanted to run, and ran out of head flow. Much better results with port work. All our D ports I run are now are 280 cfm or better with RA 4 ports or bigger. I don’t think a really high compression stock port size will work very good in a 455 on pump gas, would need 93 for sure to keep the cam from out running the heads. My pump gas 461 is a 11:1, the 6x-4 heads flow 291@28”, 224 exh, Bullet SR cam.

Most think that the HP gains are to small from the added compression to be worth the risks, most sensible engine builders won’t go there. I think just the thermal and volumetric efficiency are worth the efforts. But it only takes one thing to be overlooked and you end running more octane than originally planned. I did a cam for a friends 455 the compression was suppose to be 9.8. He wanted fo run on 87. I helped degree the cam in and I noticed the pistons where way down at TDC. Measure it at about .030” down, refigured his compression and it was in the lower 9s. He thought it was a good thing becuase it dropped the compression down, I told him it wasn’t going to work out how he was expecting (bad quench). He is determined to get it to run on 87, been helping him on it some. He may get it to run on 87, but it is not there yet. If you get to the point you get a compression target and want to run something by me, shoot me a PM. I enjoy designing high compression pump gas stuff.


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Old 07-16-2021, 06:50 AM
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Quote:
Originally Posted by Jay S View Post
Just my opinion. But if I have a set of high compression heads and spent a bunch of time and money on with port work, valves, guides , ect….I would take a hard look at cutting a symmetrical dish in the flat tops to drop the compression some and run the 48s over starting over again on some lower compression heads. If it is a balanced rotating assembly I would figure the mass loss from the dish and figure the effects on balancing, might be ok yet. That or buy appropriate pistons and maybe sell those pistons and get some pistons that will put the compression in a range that works better. I don’t like doing things twice but I would rather do that than start on another set of heads. Here it is $170 to rebalance, that won’t go very far rebuilding heads, let alone port work, even if it is a DIY scenario. Our best pump gas results (so far) have been with symmetrical dished pistons over flat tops, D shape, or domes. Maybe more factors at play there though. FWIW

I mostly shoot for between 10 to 11 compression on my cast iron heads with a lot of port work in Pontiacs 450 + cid for 87 to 91 octane. FWIWz…I don’t think I am quite to the point I am at 11:1 for 87. I was looking at the new Progression Ignition distributer that you can modified the timing curve and it connects via blue tooth with a smart phone. I think that is my next step to get to 87 on the 11:1 street engines. But I think I will carry the oem HEI in the trunk, just in case…Lol.

Totally stock d port 455 on 91 octane we have been a 10.4 SCR. Might have ran on 87, never tried it. Cam was big for the head flow, it didn’t run great. It dropped the DCR to low for the RPMs the cam wanted to run, and ran out of head flow. Much better results with port work. All our D ports I run are now are 280 cfm or better with RA 4 ports or bigger. I don’t think a really high compression stock port size will work very good in a 455 on pump gas, would need 93 for sure to keep the cam from out running the heads. My pump gas 461 is a 11:1, the 6x-4 heads flow 291@28”, 224 exh, Bullet SR cam.

Most think that the HP gains are to small from the added compression to be worth the risks, most sensible engine builders won’t go there. I think just the thermal and volumetric efficiency are worth the efforts. But it only takes one thing to be overlooked and you end running more octane than originally planned. I did a cam for a friends 455 the compression was suppose to be 9.8. He wanted fo run on 87. I helped degree the cam in and I noticed the pistons where way down at TDC. Measure it at about .030” down, refigured his compression and it was in the lower 9s. He thought it was a good thing becuase it dropped the compression down, I told him it wasn’t going to work out how he was expecting (bad quench). He is determined to get it to run on 87, been helping him on it some. He may get it to run on 87, but it is not there yet. If you get to the point you get a compression target and want to run something by me, shoot me a PM. I enjoy designing high compression pump gas stuff.
Alot there, thanks. My running engine has 38cc dish (Ross blower pistons) and figured 9.0:1 which is too low. Idles barely good enough but the rest of the performance is quite good, along with low 12s on 89. 87 on the street all day.

I really wonder about compromising the quench with two head gaskets for mid/high 9s:1 Compr and having the quench gap go from .040 to .080 with Flattops and Ram III quench surface. Just has to be on par/better than the quench left from the diameter of a 38cc dish.

And you are correct about the DIY sweat equity into the 48s; also they were pulled when running low-12s, and owned since ~1984

@ Jay S; yes, the Cometics are the get outta jail for fee. What can you say about "performance" with .140" thick head gaskets?

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Sold 2003: 12.00/112MPH/1.61 60'/26"x3.31:1/10"/469 #48/245-255-110LSA/Q-Jet-Torker/3650Lbs//18MPG 94oct
Sold 1994: 11.00/123MPH/1.50 60'/29.5"x4.10:1/10"/469 #48/245-255-110LSA/Dual600s-Wenzler/3250Lbs//94oct

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Old 07-16-2021, 09:13 AM
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I am certainly not a fan of loosing the quench. It seems like once the quench is around .070” for most engines the quench looses it’s effectiveness and increasing the quench distance more yet wasn’t noticeable over the marginal quench. Would rather make efforts to deal with the bad quench up front than try to nurse an engine along with to high of compression and a marginal quench. Poor quench higher compression engine I would keep at least 10 degrees more on the exhaust side. Doesn’t cure end gas issues, but it seems to help manage it. Going to act more like a open chamber. FWIW…We are every bit as high on compression for pump gas with open chamber heads and other engines with no quench.


Unless it was a unbelievable smoking deal on some 92-96 cc head, before letting those ported 48 heads go I would sell the flat pistons and get some pistons with a good dish. I know DSS has a nice 27 or 28 cc D dish.. 455 pistons in the photo look like nice pistons, selling them, buying dished pistons and not having to get the expensive thick Cometics would be what I would try to do first. I would do the thick cometics if that fell thru. Rather let the pistons go before I ground on another set of iron heads. Lots of guys don’t realize how much work it is when you do extensive porting.

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Old 07-15-2021, 02:22 PM
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Quote:
Originally Posted by Half-Inch Stud View Post
Working my Spare 455 +030, and have flattops and "48s".
BOP 1-piece Rear Seal in, Forger 4.21" Stroke, 3.25" Mains TQ'd with Factory Bolts. 1973 2-Bolt Block.

Wondering what Octane is needed to drive on the Street THESE DAYS.
When you say "drive it on the street", are you talking about long distance driving? Or just a weekend toy?

How much compression have you figured it'll have?

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Old 07-15-2021, 03:57 PM
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A buddy with 48s on a 428 short block WHEN the head gaskets held ran good. Cranking pressure way in the 200s!

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Old 07-15-2021, 04:35 PM
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Jay,
What (big)cam would allow HIS's combo to work???
From reading here. most 455 pistons are very close to flush???


I have some big chambered 4X's and a set of 7M5's. Only keeping them for cores.
If you and the canned ham get in my neighborhood???

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Old 07-15-2021, 04:58 PM
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I'm not worried about picking a cam. Cam worry is break-in and run long highways with all the lobes.

TWO headgaskets have crossed my mind, but the squish zone is like 80 mil at TDC.

We got the canned ham to east OK last year and went South to TX and back to Huntsville. Nice trip but a bust for property ideas.

Low compr heads are nearby (surely but condition is hobo old).

Think my running Low-Compr engine ends up in a 95 Lincoln for Tow-travel, IF the spare 455 build can run in the GTO with pump gas. Again the TWO headgasket deal is tempting.

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Old 07-15-2021, 06:31 PM
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You can’t get it under 11:1 with those parts if you wanted to mill 20cc dish in pistons but you don’t want to affect your balance job. I did a calculation with .052 head gaskets and it was still over 11:1. Some street cars run 110 just can’t get to far from home

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Old 07-15-2021, 09:09 PM
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I'm not sure it will be ok. My experience is wifh a 428 using 62 heads. it needed something to boost the octane up once the motor was warmed up. If i could keep the temps in the 160-170 range i didnt hear it detonating.

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Old 07-15-2021, 09:34 PM
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6X-4's is the way to go...

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Old 07-15-2021, 09:36 PM
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Quote:
Originally Posted by FrankieT/A View Post
6X-4's is the way to go...
This.

Detach yourself from the #48 heads.

Pump gas operation will be all but guaranteed.

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